Puffin Golden Globe 2022
Key to the design of the electrical system on Puffin is the choice of battery technology. When we looked at the details of the race it became clear that the choice of battery technology needed some thought.
The race will take Ian thorough some remarkably diverse conditions from the heat of the tropics to the terrifying storms and cold temperatures of the Southern Ocean. Looking at the electrical system on Puffin when she arrived in Pwllheli the batteries were destroyed.
So, what are our choices?
Lithium: This is not a choice; race rules forbid the use of Lithium Batteries. From what we understand this is primarily based on safety. For this application we would not have chosen Lithium as an option. The main reason is that you cannot charge Lithium Batteries below 5 Centigrade. Under normal circumstances we can use excess power from the generation source to heat the batteries. However, we are looking at diverting excess power to heat the skipper.
Lead Acid: In the lead acid group we have wet cells, sealed, Gel & AGM. Wet cells are out for boats. The idea of Sulphuric Acid sloshing around in extreme conditions is a scary thought. Again the race organisers are safety conscious and understandably wet cell batteries and quite rightly seen as not being suitable. Sealed batteries are not an attractive idea either, again for the same reasons, they may be sealed but they still have sulphuric acid in liquid form. With Gel & AGM batteries the acid is held either in the form of a GEL or absorbed into a glass fibre mat. Without going into finer details all these technologies require that the batteries be charged to 100% on a regular basis. Failure to charge to 100% will reduce the capacity of the batteries. Discharging to low levels can cause permanent damage. To charge to 100% an absorption period of up to 8 hours would be needed. This cannot be guaranteed, and there is not the option to stop off for a quick battery change.
Lead Carbon: We have used this technology in a variety of applications where Lithium cannot be used. These applications are in demanding environments or where the cost of Lithium is beyond the budget. The main benefit of Lead Carbon batteries is that they can be partially charged without loss of storage capacity. You can use up to 80% of the capacity without damage unlike GEL & AGM where a discharge of more than 50% is not recommended to prolong battery life. They are robust, essential on this journey. They can even be completely discharged without serious damage (although we would not recommend this on a regular basis). The downside is that they are heavy, as it turns out, on Puffin this is an advantage as ballast is needed at the stern of the boat.
Safety: Lets face it if you are going to store energy there are going to be hazards. Petrol & gas are simply explosive, diesel is a lot safer and like petrol & gas, require a complex engine to convert the stored energy into electricity, not ideal in a hostile environment. Lithium batteries are perceived (somewhat harshly) as being hazardous. Lead acid wet cells are clearly dodgy with a bucket full of sulphuric acid sloshing around. Gel and AGM are seen as being a lot safer as the electrolyte is held either absorbed into a glass matt or as a gel. Lead carbon are even safer. They hold the electrolyte in the same way as a GEL battery (race organisers are happy with this). The reason that they are safer is that when the GEL & AGM batteries start to suffer and dramatically lose capacity due to partial charge and discharge the Lead carbon will not suffer the same fate. GEL, AGM & Lead Carbon Batteries all have the same material safety data see here. Battery Data Sheet